1. Field of the Invention
This invention relates generally to disk apparatuses and, more particularly, to a disk apparatus for reproducing information out of a disk having record at lands/grooves, such as an ASMO (Advanced-Storage Magneto-Optical) disk.
2. Description of the Prior Art
In the conventional disk apparatus of this kind such as DVD or CD, the optical pickup is corrected for focus-offset deviation by adjusting the focus offset in a manner maximizing the RF signal or minimizing jitter in the RF signal.
Meanwhile, there is disclosed as one example a conventional disk apparatus of this kind in Japanese Patent Laid-Open No. H8-7300 [G11B 7/09, G11B 7/007] laid open on Jan. 12, 1996. In this focus offset adjusting device, an offset amount is detected from a reproduced-signal envelope voltage in positive and negative sections of a wobbling signal, thereby outputting offset voltage to correct deviation in the focus offset. This offset voltage is added to the focus error signal, thereby automatically adjusting the focus offset.
However, in the former case, where an ASMO disk is used, no RF signals are recorded thereon. Consequently, focus balance adjustment is impossible to perform in correcting focus-offset deviation. In the latter case, because the envelope voltage is sampled using the reproduced signals from the VFO region, focus balance adjustment can be implemented for only the disk having record at the land.
Therefore, it is a primary object of the present invention to provide a disk apparatus capable of setting focus offset values optimal for the respective land and groove.
The present invention is a disk apparatus for reproducing information out of a disk having record at lands/grooves, comprising: an extractor for illuminating and converging laser light to the disk and extracting fine clock mark signals out of laser light reflected upon the disk; and a setter for setting focus offset values optimal for the land and the groove based on mean values of the fine clock mark signals.
This disk apparatus can reproduce information from a disk having record at lands/grooves. For example, the laser light emitted from the laser diode is converged and illuminated onto a reproducing surface of the disk. The light reflects upon the disk reproducing surface and turns into reflection light from which fine clock mark signals (FCM signals) are to be extracted. Based on a mean value in level of the FCM signals, the setting means sets an optimal focus offset value. The setter provides setting of optimal focus offset signals respectively for the land and the groove. When reproducing with the disk, focus offset values may be switched that have been respectively set depending on a track (land/groove).
According to the invention, optimal focus offset values can be set respectively for the land and the groove, thus providing an optimal reproduced signal.
In one aspect of the invention, the setter detects FCM signal levels for focus offset in positions shifted left and right (plus and minus) by a predetermined amount from a present focus offset value. Then, the difference detector detects a difference between the detected two FCM signal levels. That is, it is possible to determine based on the difference whether the present focus offset value is proper or not.
In one embodiment of the invention, a predetermined number of FCM signal levels are detected (sampled), and then the sampled FCM signal levels are averaged. Consequently, it is possible to absorb errors in FC signal levels caused due to eccentricity component of the disk.
In another embodiment of the invention, the focus offset value where the two FCM signal levels are minimized in difference is determined as an optimal focus offset value.
In still another embodiment of the invention, in a range where a mean value of FCM signal levels is equal to or greater than a predetermined level, a first shifter shifts (scans) a predetermined amount per time from a current focus offset value toward a maximum reference value, i.e. the focus offset value is incremented in order, each time of which a difference is detected in the above manner. Reaching the maximum reference value, a second shifter scans a predetermined amount per time from the present focus offset value toward a minimum reference value, i.e. the focus offset value is decremented in order, each time of which a difference is detected. Accordingly, an optimal focus offset value is to be determined by a focus offset value at which a difference thereof assumes a minimum of all the differences detected throughout the range.